Southern California -- this just in

Whitney Houston death report still weeks away, sources say

Investigators said it will take several more weeks to determine a final cause of death for Whitney Houston.

Sources familiar with the probe said the investigation is still ongoing and that there is no precise date for when it will be completed.

Beverly Hills police officials have said they don't believe foul play was involved, but sources said investigators cannot give a cause of death until all toxicology tests are back and detectives have concluded all interviews.

Investigators have served subpoenas on doctors and pharmacies as they try to determine whether prescription drugs played a role in the singer's death.

Authorities collected several bottles of prescription drugs from Houston's suite at the Beverly Hilton Hotel, where she was found dead Feb. 11 in a bathtub. But officials have said the amounts of drugs did not seem unusually large, leaving it unclear whether the medications had anything to do with her death.

The death certificate, released this month, says the manner of death was "pending investigation."

The sources, who spoke on the condition of anonymity because the case is ongoing, said the determination could come by the end of March but that it remains unclear exactly when all the tests and interviews would be completed.

Houston's sister-in-law and manager described to Oprah Winfrey the scene in a Beverly Hills hotel suite when the singer was found dead.

Patricia Houston told Oprah Winfrey in an interview broadcast Sunday said she heard screams coming from Houston's room and when she arrived she saw one of the singer's assistants in tears.